Inertial switches movable between open and closed conditions in response to accelerations are well known and have been used in a wide variety of applications. Conventional inertial switches include inner and outer electrically isolated terminals. A spring is attached to the inner terminal and a mass is coupled to the spring. When the inertial switch undergoes an acceleration above a threshold value, the spring and mass system undergo movement which results in the inner and outer terminals being electrically connected thereby closing the inertial switch. The closure of the inertial switch can be used to trigger another event.
Unfortunately, these conventional inertial switches which include separate spring and mass systems are expensive to manufacture and are prone to mechanical failure. In an attempt to overcome these disadvantages, an inertial switch obviating the need for a separate mass has been developed and is described in U.S. Pat. No. 4,201,898 to Jones et al. The Jones et al. inertial switch includes a resilient spiral spring attached at one end to an adjustable post. The free end of the spiral spring is movable to contact an outer housing surrounding the spring to close the inertial switch when the inertial switch undergoes an acceleration.
Although the Jones et al. inertial switch does not have a mass coupled to the spring making it less prone to mechanical failure, the use of a spiral spring which moves to contact the outer housing in response to bending stresses applied to the spring as a result of an applied acceleration, decreases the sensitivity of the inertial switch. Accordingly, improved inertial switches which are inexpensive to manufacture, sensitive and exhibit longevity are sought.
It is therefore an object of the present invention to provide a novel inertial switch.